I was able to unclog grease fittings on my tractor that bed stopped up for a long time. The WD-40 that I forced into the bearings, dissolved the old grease. allowing me to get new grease in.
This tool is designed to force motor oil or grease into plugged grease fittings. I was working on old spring shackles and was not able to get them to open up. Ended up replacing the spring shackles. This tool is held against the fitting and struck with a hammer to force the oil or grease into the fitting. A tool that attaches to the fitting like a grease gun may work better, especially if you are using penetrating oil to cleanout out or open up the grease fitting. I'm glad I tried the tool and will keep it in my tool box, but it always helps to use the right tool for the job.